Although all cells in the human body contain the same genetic material, the same genes are not active in all of those cells. Alterations in gene expression patterns can have profound effects on biological functions. These variations in gene expression can be at the core of altered physiologic and pathologic processes. Therefore, identifying and quantifying the expression of genes in cells can aid the discovery of new therapeutic and diagnostic targets.
To date there are several techniques available that allow the detection of the expression level of multiple genes in a complex sample at one time. Most of these technologies employ, DNA microarrays, devices that consist of thousands of immobilized DNA sequences present on a miniaturized surface that have made this process more efficient. Unfortunately, despite the miniaturization of array formats, this method still requires significant amounts of the biological sample. However, in several cases, such as biopsies of diseased tissues or samples of a discrete cell type, the biological sample is in limited supply. In addition, the kinetics of hybridization on the surface of a microarray is less efficient than hybridization in small amounts of aqueous solution. Moreover, while methods exist to estimate the amount of nucleic acid present in a sample based on microarray hybridization result, microarray technology thus far does not allow for detection of target molecules on an individual level, nor are there microarray-based methods for directly quantifying the amount of target molecule in a given sample.
Thus, there exists a need for accurate and sensitive detection, identification and quantification of target molecules in complex mixtures.